This invention relates to upper knife releasing devices for overlock sewing machines, and more particularly to an upper knife releasing device suitably employed in the overlock sewing machine for use in forming overedge stitches, double chainstitches, and specially established stitches other than those.
When the overedge stitches are formed by the overlock sewing machine, the workpiece or work is cut or trimmed by a slide movement of upper and lower knives. A work cutter or trimmer to be used to this end has been heretofore well known as what is arranged so that the upper knife is supported by vertically swingable member which is vertically driven by an upper knife drive element or means that uses the main shaft as a drive source.
A conventional approach has been heretofore so made, if such overlock sewing machine of this class is used in forming either overedge stitches by way of work cutting or both of double stitches and special established stitches by way of no work cutting, as to render the upper knife inactive to this end.
The above-described conventional sewing machine is disadvantageous in the following points: Even when the upper knife is moved away from the lower knife by turning it with respect to the upper knife rocking arm, the latter is left turned. The upper knife rocking arm is not only hazardous but also obstructive over the sewing machine table during sewing work, thus limiting the work space. More specifically, it is rather difficult to thread the needle and to replace the needle.